1. Field of the Invention
The invention concerns an opto-electronic device for acquisition of images of codes in one and two dimensions.
2. Description of the Related Art
Numerous types of two-dimensional codes have been in use for some years. The main advantage of this new type of code in relation to the traditional bar codes (1D or stacked 1D) is that it contains a much greater density of recorded information for the same useful surface.
The appearance of this new generation of codes has, of course, led to the realization of new types of opto-electronic devices, or readers, which are capable of processing the two-dimensional codes while retaining the possibility of processing the conventional bar codes.
Such readers comprise, firstly, an electronic sensor for acquisition of images of variable size (CDD technology or other), an illumination source to illuminate the codes and to permit the acquisition of the images on the electronic sensor, and an image-processor adapted to control the electronic sensor and the illumination source and to ensure the decoding of the images formed on said electronic sensor.
Moreover, the acquisition and processing of the images of the current readers are principally composed:
of a conversion module permitting the images emitted from the electronic sensor to be digitized, that is to say, permitting this image to be coded in a certain number of levels of gray, generally 256, and permitting a constant flow of digitized data to be provided at the pixel frequency, PA1 of a memory module permitting the storage of the digitized data and comprising one or more image planes, PA1 and of a processing module performing the set of operations necessary for reading and decoding the two-dimensional code. PA1 an analog/digital converter to convert the analog data emitted from the photosensitive matrix into a stream of digital data coded in a predetermined number of levels of gray, PA1 a preprocessing module including, for example, cabled processing units, adapted to ensure low-level processing of the stream of digital data and to provide, on the one hand, a binarized representation of the images formed on the electronic sensor and, on the other hand, primary data which are characteristic of the captured codes, the preprocessing module also including a buffer register for temporary storage of the binarized images and of the primary data, PA1 a first programmable processing module comprising: PA1 and a second programmable processing module comprising: PA1 a preprocessing module in the form of cabled processing units, acting in synchronous mode at the pixel frequency on the flow of the data emitted from the digitization stage and implementing simple operations for processing of images permitting a quantity of information to be obtained at the output of the preprocessing module that is sufficient for obtaining the subsequent decoding of the images but nonetheless clearly less than the quantity of information that storage of the initial image would necessitate, PA1 programmable modules acting in asynchronous mode on the data emitted from the preceding module and stored in alternative manner in two memories and realizing more complex processing operations culminating in the obtaining of normalized data that are representative of the information "coded" in the captured codes. PA1 a lines memory block, adapted to store the digital data in the form of a drop window of (x) consecutive lines each comprising n pixels, PA1 a binarization circuit adapted to code the digital data in binary form as a function of an open-ended threshold calculated for each datum processed, taking account of the neighborhood of the (x, x) data surrounding said datum. PA1 a first processing submodule comprising the binarization circuit and the circuit for detection of signatures and adapted to supply a binary image and the Cartesian coordinates of the specific signatures of the codes to the buffer register, PA1 a second processing submodule comprising successively: PA1 the binary image, PA1 the reduced image and the image of the contours, PA1 the data relating to the straight-line segments and to the specific signatures of the codes.
On the basis of such an architecture the current portable opto-electronic devices operate on matrices having a maximum size of about 800.times.600 pixels at a rate on the order of three images per second. However, as a result of the constant progress made by the micro-electronic industry, offering ever more significant possibilities and powers of calculation, new devices possessing enhanced performance characteristics in terms of rate of calculation are in the course of development. A gain in some units on the order of a factor of 5 has been announced.
However, it is advisable to note that this possibility for enhancing performance characteristics in terms of rate of calculation turns out to be limited in practice on account of the architecture, described above, of the image acquisition and processing module, by reason of the time needed by the processing module to perform, between two acquisitions, the reading and decoding operations for each captured code.
Furthermore, there is, on the other hand, no rational solution at the present time permitting the size of the processed images to be notably increased. The increase in the size of the processed images actually turns out to be much more problematic, for the calculating power necessary for the processing increases as the square of the enlargement factor of the original image: doubling the size of the image therefore necessitates a quadrupling of the calculating power.
Now, for the architecture, described above, of the current opto-electronic devices any increase in the calculating power is translated into a notable increase in the necessary memory size, and therefore into a notable increase, on the one hand, in the requirements in terms of electrical consumption, and on the other hand in the necessary volume for installation of the memory blocks.
In practice such constraints of physical nature and of consumption explain, particularly with regard to the portable opto-electronic devices, the limitation of the size of the matrices to the values stated above, that is, to say, 800.times.600 pixels.
However, it turns out that the two-dimensional codes tend to "code" more and more information, but on surfaces that are more and more reduced, so the increase in the maximum size of the matrices appears to be absolutely essential.